Examination of the postmortem alteration of dental enamel – combined analytical approaches and pre-treatment method standardisation

Oxygen isotope (δ 18 O) analysis of carbonate-bearing hydroxyapatite from human dental enamel is widely used in archaeological studies because it reflects the isotopic composition of ingested water. However, certain postmortem alteration processes may affect the δ 18 O signatures of the carbonate (δ 18 O c ) and/or the phosphate (δ 18 O p ) components. This study investigates the diagenetic changes to human dental enamel samples from two Hungarian archaeological sites using oxygen isotope measurements, as well as X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Although crystallinity changes are observed, the primary causes of disequilibrium between δ 18 O c and δ 18 O p appears to be the incorporation of secondary carbonate and the isotopic exchange between enamel carbonate and soil water. FTIR peak-area ratios proved to be more sensitive indicators of alteration than peak intensities. The comparison of pre-treated and untreated samples confirms that the chemical treatment of dental enamel can amplify disequilibrium δ 18 O shifts in the carbonate component when alteration is present. The results of combined phosphate and carbonate δ 18 O analyses support the method of δ 18 O c analysis without enamel pre-treatment to remove organic content. These findings emphasise the importance of both sample preparation procedures and structural analyses of dental enamel prior to the interpretation of isotopic data.